Current-regulating device or resistance applicable for electric lighting or heating.



W. SUMNER, CURRENT REGULATING DEVICE OR RESISTANCE APPLICABLE FOR ELECTRIC LIGHTING 0R HEATING. APPLICATION FILED JAN.5,1912

1,087,683. Patented Sept. 3,1912.

a J x UNITED STATES PATENT OFFICE.

WILLIAM SUMNER, 0F LIVERPOOL, ENGLAND.

CURRENT-REGULATING DEVICE 0R RESISTANCE APPLICABLE FOR ELECTRIC LIGHTING OR, HEATING.

Specification of Letters Patent.

Patented Sept. 3, 1912.

Application filed January 5, 1912. Serial No. 669,667.

To all whom it may concern:

Be it known that I, WVILLIAM SUMNER, a subject of the King of Great Britain, residing at 31 Moira street, Liverpool, England, have invented certain new and useful Improvements in Gurrent-Regulating Devices or Resistances Applicable for Electric Lighting or Heating, of which the iollowing is a specification.

This invention relates to improvements in electric current regulating devices or resistances and is especially applicable for use in connection with incandescent lamps whereby the current supplied to. the lamp may be regulated as required to any minimum and the luminosity of the lamp filament varied accordingly, or the device may be used as an electric heater.

Resistance devices or dimmers for electric lamps are known in which the medium of which the resistance is composed con- :ists of a loose mixture of powdered mica, sand and graphite, the resistability of the medium being varied according to the degree of compression applied thereto. Such a resistance is however unsatisfactory inasmuch as there is not sufficient elasticity in the composition to cause it to restore itself to its normal condition when released from compression, and further, the several constituents ofthe mixture, even if intimately intermixed in the first instance, are apt in course of time owing to vibration or the continued operation of compressing and releasing, to separate themselves and thus destroy the homogeneous character or evenness of the mixture, thereby causing the effectiveness of the resistance to be impaired. Resistances of this class are also known comprising a mixture of asbestos and carbon in the form of a pad adapted to be compressed for the purpose of varying the resistance. Such a preparation is, however, unsatisfactory owing to the fact that the small percentage of carbon which is requisite to effect the desired control of the comparatively sinall current passing through an incandescent lamp, cannot, by commercial methods, be evenly incorporated with the asbestos. Unless the carbon is very evenly distributed throughout the mixturecomposing the resistance it is impossible to obtain the nicety of or minute control of the current necessary to effect say, a gradual dimming of the luminosity of an electric incandescent lamp as when pressure is applied to the resistance a possible localization of the path or". the current through the resistance may be set up, in which case a faint glow of the filament of the lamp would be impossible so long as any pressure was maintained and on the removal of the pressure arcing may result.

In the making of electric resistances from a series of sheets of fibrous material it has been proposed to coat the fibrous material on each side with coal tar, the sheets being subsequently heated to carbonize the fiber, but in this my invention the resistances after impregnation with the mixture hereinafter described are heated to increase the resiliency of the said resistances.

The present invention is directed to obtaining a resistance pad or the like which shall be characterized by an even and comparatively rare distribution of the carbon particles throughout a fibrous body or support, and which shall have a considerable elasticity. To effect this, I make a mixture of finely ground plumbago or analogous preparation of carbon reduced to the condition of an impalpable powder, and finely powdered chalk or the like insulating medium in the proportion of about 25% of plumbago to 75% of chalk by weight.

This mixture is then intimately incorporated with the fibrous material, preferably asbestos fiax, in any suitable manner, say by revolving them together in a receptacle, or treating them in a mixer until the asbestos is thoroughly impregnated with the mixture. Any excess of the plumbago and chalk is then shaken out. Such a method of treating the asbestos with a mixture of plumbago and chalk insures a very even and comparetively rare distribution of the particles of plumbago throughout the asbestos to be effected'in a manner practicable on a commercial scale. The asbestos so prepared is then spun into yarn and coiled, wound or otherwise made up into pads or the like which, in a suitable construction, may be mounted within an asbestos, fiber or other fireproof shell or casing closed at one end by a contact plate or the like connected to one end of the electrical conductor of the circuit to be controlled.

The accompanying drawings show by way of example several methods of preparing a resistance pad from coiled or wound yarn and of mounting it within a box or caslng.

Figures 1 and 2 are an elevation and plan respectively of. a pad produced in accordance with this invention by simply coiling up an impregnated asbestos yarn orcord. Figs. 3 and 4 show the successive stages of a modified arrangement in which the pad is prepared by transversely winding the spun yarn upon a base plate. Figs. 5 and 6 are an elevation and plan respectively of a further modification in theconstruction of the pad, the latter being here made from a coiled strand formed by winding the ashestos yarn upon a wire core. Fig. 7 is a longitudinal section showing a single pad respectively capable of being connected up.

to the leads or terminals 6, e of the circuit to be controlled. The contact disk 0 has preferably a direct connection with the lead or terminal 6 while the connection between-the contact disk d is preferably efiected through a spring f connected to the lead or terminal and adapted to be pressed against the outer side of the plate a? by a regulating screw 9 or other compression device, by the operation of which the springis pressed against the plate d and the compression of the pad efiected, the current passing through the i said pad to thecontact plate 0.

The asbestos or fibrous material after being impregnated with the mixture of plumbago and chalk is spun into a yarn or cord h which is then wound to the required shape of the pad or resistance. Such a method of forming the impregnated asbestos into a yarn and winding it into a pad achieves a very even distribution of the plumbago throughout the mass of the pad and gives to the pad a very considerable elasticity, while the method also lends itself admirably to the production of pads in great quantities and on a commercial scale by unskilled labor, each pad having the same degree of resistance. If desired, the impregnated yarn may be wound on a wire core 11, Figs. 5 and 6, which is then subsequently coiled to form a pad or the like, the core being left in or removed, orthe spun yarn 72, may be wound transversely to' form several layers around a metal or other disk or plate 70. Figs. 3 and 4, a series of such pads being, if desired, superimposed to form a composite near, as

pad. The asbestos or other fibrous yarn may be impregnated with the plumbago preparation after it is in the form of a yarn, but it is much preferred to first impregnate the fibrous material and then spin it into the yarn or cord. The pads in whatever way prepared are supported by metallic plates or disks as above described.

A lamp connected to the regulating device represented in Fig. 7 receives the maximum amount of current when the resistance pad is compressed to the full extent by the operation of the screw g, but by rotating the said screw in 'the direction proper for relaxing the pressure on the pad, the resiliency of the same efi'ects its expansion, thus increasing the resistance and causing a'diminution of the brightness of the light corresponding with the extent. to which the pressure is relaxed.

The asbestos shell or casing b may be inclosed in a porcelain casing or otherwise, in the cover of which the regulating screw may be carried. To obtain the best results it is necessary that the pad should not be.

completely released from compression even when the faintest glow is required on the lamp or the smallest current passing through the pad, and this result can only be obtained when the particles of carbon areso equally distributed throughout the asbestos that no matter what the degree of compression on the pad its substance will maintain an even conductivity throughout at all stages though this conductivity as a whole varies in accordance with the compression. Such homogeneity in the conductivity of the pad is broughtabout by the-rare, but equal, distribution of the carbon particles owing to their being first mixed with the chalk or the like preparatory to being incorporated with the asbestos, and also owing to this rare but equal distribution the current may be controlled to a minimum and practically cut oii', the pad still being under some compression.

The resiliency of the pad, which is an essential feature of its successful working, may be increased by heating the pad after being prepared with the plumbago and chalk, to a white heat and then allowing it tocool. In the case of adapting the device for use with currents of large amperage, or for heating resistances, I may mount the pads a in a series one upon another, as shown in Fig. 8, and alternated with metallic disks d between each pad.

A pad produced in the manner described may be made of very, small dimensions, say, about five eighths of an inch diameter by one eighth deep for the control of an ordinarv incandescent lamp, thus lending itself to the construction of a very compact type of device.

Although the invention has been described with some special reference to incandescent lamps it may be applied to the control of other forms of electric lighting or to the control of electric currents generally and the resistances may constitute independent devices introduced into the circuit to be controlled or they may be adapted vto form parts of switches or other current controlling devices.

Having now described my invention what I claim as new and desire to secure by Letters Patent is The process of producing a resistance medium which consists in impregnating fibrous material with an intimate mixture 5 of'carbon and finely divided insulating material, spinning the impregnated fibrous material "into a yarn, coiling the yarn to form a pad, heating the pad to a high temperature, and finally cooling the heated pad.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

. WILLIAM SUMNER.

Witnesses:

FRANK JONES, G. F. WOUNDALL. 

